Early Monsoon Arrival in 2025
- Monsoon reached Kerala on May 24, a week early (normal date: June 1).
- This is the earliest onset since 2009, which saw monsoon on May 23.
Relevance : GS 1(Geography – Monsoon)
Is Early Onset Predictable?
- No definitive “secret sauce” behind early arrival; highly variable.
- Early onset doesn’t guarantee a good monsoon; late onset (>2 weeks) usually correlates with deficit rainfall.
- Onset predictions are complex and uncertain.
Scientific Understanding of Onset
- No unified theory on monsoon onset; multiple interacting systems.
- Trough movement from NW Pacific → Andaman Sea → Bay of Bengal → Kerala is key but poorly understood.
- El Niño/La Niña offer no reliable predictability for onset timing.
Climate Change and Delay in Onset
- Onset has been systematically delayed since 1970s, potentially due to:
- Natural decadal variability.
- Global warming’s influence on monsoon systems.
- However, early onsets still occur despite general delay trend (e.g., 2025).
Comparing 2025 with 2009
- 2009 was a mild El Niño year and ended in monsoon drought.
- 2025 has seen record warmth (1.2°C above pre-industrial levels).
- SST anomalies in 2024 showed mixed El Niño/La Niña traits, complicating forecasts.
- Currently, neutral ENSO and IOD conditions predicted.
External Drivers of Early Onset
- Increased pre-monsoon cyclones may be pulling monsoon trough northward earlier.
- Western coast low-pressure systems likely helped early arrival in 2025.
- Cyclonic activity linked to Arctic warming and wind shifts in Arabian Sea.
- Typhoons in Pacific can delay onset by pulling moisture away.
Forecast Complexity
- Even with good onset prediction, seasonal distribution still erratic.
- Early onset doesn’t imply:
- Normal seasonal rainfall.
- No floods/droughts within season.
Changing Rainfall Patterns
- Monsoon withdrawal is shifting; SW and NE monsoons merging in regions.
- Intra-seasonal rainfall is uneven – both floods and droughts increasing.
Conclusion
- Causes of early onset remain uncertain and multifactorial.
- Ongoing need for:
- Deeper insights into monsoon dynamics.
- Better models to include climate change, ENSO, cyclones, and Arctic impacts.
